1. Field of the Invention
The present invention relates to a lens barrel including a surface wave motor to drive a photographic lens, and, more particularly, the present invention relates to a lens barrel having a surface wave motor and a rotation angle conversion device to transmit a rotation angle of a hand-operated unit to a rotation angle of a fixed member of the surface wave motor.
2. Description of the Related Art
A lens barrel having a built-in surface wave motor is known, for example, as disclosed in Japanese Laid-Open Patent Publication JP-A-8-98191. The lens barrel having a built-in surface wave motor disclosed in JP-A-8-98191 includes a photographic optical system, a fixed member, a hand-operated member, a fixed tube and a mode selection member. The fixed member and the hand-operated member are integrally coupled such that rotation with respect to the fixed tube is possible. The mode selection member is an electrical switch to select a mode of focus adjustment.
In operation of the known lens barrel, when a manual focus adjustment mode is selected by the mode selection member, a moving member and the fixed member of the surface wave motor become integral, and the photographic optical system is driven by rotation coupled to the manual operation of the hand-operated member. Because of the relationship between the fixed member and the moving member, when in the manual focus adjustment mode, the contact surface of the moving member and the fixed member does not become damaged, and is capable of driving the photographic optical system. Moreover, when an automatic focus adjustment mode is selected by the mode selection member, the fixed member is fixed relative to the fixed tube, and the photographic optical system is moved by the rotation of the moving member.
FIG. 3 is a cross-sectional diagram of a prior art lens barrel having a built-in surface wave motor. FIG. 4 is a partial side view diagram, seen externally of the lens barrel in an axial direction, of a roller of a prior art lens barrel having a built-in surface wave motor. FIG. 5 is a cross-sectional diagram of an electrical power supply unit of a prior art lens barrel having a built-in surface wave motor. FIG. 6 is a schematic block diagram of a prior art lens barrel having a built-in surface wave motor.
Furthermore, the state of the lens barrel shown in FIG. 3 is in an automatic focus adjustment mode. The mode changeover switch 20 sets the automatic focus adjustment mode, in which the optical system L2, L3 for performing focus adjustment is driven by the rotational force of the surface wave motor Mo (FIG. 6).
As shown in FIG. 3, the optical system L2, L3 for performing focus adjustment is supported by a lens support tube 2, and performs focus adjustment by movement in the optical axis direction. The lens support tube 2 is located in the internal circumference of a central middle diameter portion 1a of a fixed barrel 1, and is fitted movably in the optical axis direction. A projecting pin 3 is mounted in the outer circumference of the lens support tube 2. The projecting pin 3 passes through a guide groove which is parallel to the optical axis and is disposed in the central middle diameter portion 1a of the fixed barrel 1. The front end of the projecting pin 3 engages a cam groove 4a disposed in the inner circumferential surface of a cam ring 4.
The inner circumferential portion of the cam ring 4 fits onto the outer circumferential portion of the central middle diameter portion 1a of the fixed barrel 1. A circular circumferential groove 4b is formed in the inner circumferential surface of the cam ring 4. A projecting pin 5, mounted on the outer circumferential surface of the central middle diameter portion 1a, fits, in a freely movable state, into the circular circumferential groove 4b. Because of the above arrangement, the cam ring 4 is immovable in the optical axis direction, and is rotatable in only a predetermined angular range centered on the optical axis. Moreover, a distance scale (not shown) is displayed on the right-hand side large diameter circumferential portion 4c of the cam ring 4.
A fixed element 6 of the surface wave motor Mo rotates with the optical axis as center, and generates surface waves. An inner circumferential portion of the fixed element 6 fits into an outer circumferential portion of a central small diameter portion 1c of the fixed barrel 1. A plurality of rotation shafts 26 having rotary axial lines in a direction at right angles to the optical axis are mounted in the outer circumferential surface of the fixed member 6. Freely rotatable rollers 25 are mounted on the rotary shafts 26.
A rotary element 9 of the surface wave motor Mo generates a drive force to drive the focus adjustment optical system L2, L3, rotating centered on the optical axis by the surface wave generated by the fixed element 6. The rotary element 9 is in frictional contact with the fixed element 6, and rotates freely relative to the fixed element 6 via a bearing 12. An engagement groove 9a is disposed in the left-hand side of the rotary element 9, and engages with a cooperating projection 4d disposed in the right-hand side, large diameter inner circumferential portion 4c of the cam ring 4. Because of the arrangement of the engagement groove 9a and cooperating projection 4d, when the fixed element 6 generates surface waves, the rotary element 9 and the cam ring 4 rotate integrally, centered on the optical axis, as a result of the surface wave. Moreover, a biasing member 14 places the rotary element 9 in frictional contact with the fixed element 6 via a disc 13.
A hand-operated ring 10 drives the focus adjustment optical system L2, L3 in the optical axis direction by an external operation by the photographer. The hand-operated ring 10 has its two ends respectively fitted into a large diameter portion 1d and a left-hand large diameter portion 1e of the fixed barrel 1. The hand-operated ring 10 is immovable in the optical axis direction, and is freely rotatable centered on the optical axis. An intermediate ring 7, formed of transparent synthetic resin, is rotatably disposed in an inner circumferential portion of the hand-operated ring 10.
A biasing member 11 presses on the fixed element 6 via the roller 25, and confers a predetermined frictional torque on the inner circumferential surface of the large diameter portion 1d of the fixed barrel 1, such that the fixed element 6 does not easily rotate when in the automatic focus adjustment mode. As shown in FIG. 3, the biasing member 11 is disposed between the central small diameter portion 1c of the fixed barrel 1 and the fixed element 6.
A biasing member 27 is disposed between the hand-operated ring 10 and the intermediate ring 7 in the inner circumferential surface of the large diameter portion 1d of the fixed barrel 1. The biasing member 27 presses the intermediate ring 7 via the roller 25, and causes frictional contact between biasing member 27, intermediate ring 7 and roller 25.
The roller 25 transmits the rotation angle of the hand-operated ring 10 to the rotation angle of the fixed element 6 (cam ring 4) of the surface wave motor Mo at an optional ratio. The roller 25 has an inner ring of metal and has an outer circumference covered with rubber. As shown in FIG. 4, the roller 25 is formed in two portions, with a large diameter portion 25a having a diameter Db at its outer circumferential surface, and a small diameter portion 25b having a diameter Db' (Db&gt;Db'). The outer circumferential surface of the roller 25 has a difference in diameter, changing in its external diameter in the axial direction of the rotary shaft 26. The small diameter portion 25b, having diameter Db', contacts the side surface of the intermediate ring 7, and the large diameter portion 25a, having diameter Db, contacts the side surface of the large diameter portion 1d of the fixed barrel 1.
Accordingly, when the hand-operated ring 10 is rotated, the roller 25 rotates between the intermediate ring 7 and the large diameter portion 1d of the fixed barrel 1, and the fixed element 6 rotates centered on the optical axis on the outer circumference of the central small diameter portion 1c of the fixed barrel 1. At this time, the ratio Rr of the fixed element 6 (cam ring 4) relative to the rotation angle of the intermediate ring 7 is represented by the following Equation (1), in accordance with the principle of planetary gear devices. EQU Rr=(Db.multidot.Dc)/(Da.multidot.Db'+Db.multidot.Dc) Eq. (1)
In Equation (1), Da is the diameter of the region of contact of the roller 25 with the fixed barrel 1; and, Dc is the diameter of the region of contact of the roller 25 and the intermediate ring 7.
As shown in FIG. 3, a window member 8 allows the distance scale which is displayed on the right-hand, large diameter, circumferential portion 4c of the cam ring 4 to be read out through the intermediate ring 7 made of transparent synthetic resin. The window 8 is disposed in the large diameter portion 1d of the fixed barrel 1, and is made of transparent synthetic resin.
A glass epoxy plate 15 is fixed to the fixed element 6. As shown in FIG. 5, conductive portions 15a having an annular form are disposed along the whole circumference of the fixed element 6. Because of the arrangement of the conductive portions 15a, brushes 16 slide on the conductive portions 15a, and electrical connection is possible with respect to the fixed element 6, regardless of the angular position of the fixed element 6. Furthermore, the glass epoxy plate 15 has through holes 15b disposed in positions offset from the conductive annular portions 15a. The conductive portions 15a make electrical contact with the fixed element 6 from its back surface through the conductive portions of the back surface of the glass epoxy plate 15.
A pressure plate 17 fixes the brushes 16 in a brush fixing plate 18. The brush fixing plate 18 is fixed by small screws 19 to the fixed barrel 1.
As shown in FIG. 3, the mode changeover switch 20 is slidably disposed on the fixed barrel 1, and is a switch which slides in the direction M to set the manual focus adjustment mode and slides in the direction A to set the automatic focus adjustment mode. The mode changeover switch 20 corresponds to the mode selection unit 31 shown in FIG. 6, and generates electrical signals according to the respective mode. When the mode of operation is changed to the automatic focus adjustment mode, the power supply unit 100 supplies electric power to the surface wave motor Mo.
As shown in FIG. 3, a changeover plate 21 is fixed to the changeover switch 20 by a small screw 23. A plate spring 22 is fixed to the fixed barrel 1 by a small screw 24. The plate spring 22 is disengageable in plural engagement grooves 6a located in the outer circumferential portion of the fixed element 6.
When the mode changeover switch 20 slides in the M direction to change to the manual focus adjustment mode, the changeover plate 21 moves at the same time. The changeover plate 21 then presses the plate spring 22 downward, as shown by the dotted lines FIG. 3, the plate spring 22 separates from the engagement grooves 6a of the fixed element 6, and the hand-operated ring 10 is rotatable.
When the mode changeover switch 20 slides in the A direction to change to the automatic focus adjustment mode, the changeover plate 21 moves at the same time. The plate spring 22 then returns to the initial state, as shown by the full lines in the FIG. 3, and engages with the engagement grooves 6a of the fixed element 6. As a result, the hand-operated ring 10 is prevented from rotating.
Furthermore, by setting A as the frictional torque of the fixed element 6 and the rotary element 9, B as the frictional torque of the fixed barrel 1 and the fixed element 6, and C as the torque which is necessary to drive the lens support tube 2, the condition C&lt;B&lt;A is satisfied.
The operation of a prior art lens barrel having a built-in surface wave motor will now be described below. The automatic focus adjustment mode will be described first.
As shown by the full lines in FIG. 3, when the prior art lens barrel is in the automatic focus adjustment mode, the mode changeover switch 20 is in the A position, and the engagement grooves 6a of the fixed element 6 and the plate spring 22 are in engagement. Because of the engagement between the engagement grooves 6a and the plate spring 22, rotation of the hand-operated ring 10 is prevented, and the fixed element 6 is also in a state in which it cannot rotate.
Power is supplied to the surface wave motor Mo by a control mechanism (not shown in FIG. 3) corresponding to the power supply unit 100 shown in FIG. 6, to generate surface traveling waves in the fixed element 6, thereby causing the rotary element 9 to rotate in the circumferential direction. The left-hand side engagement groove 9a of the rotary element 9 engages with the engagement projection 4d disposed in the cam ring 4. When the rotary element 9 rotates, the rotary element 9 and the cam ring 4 rotate integrally. Then, when the cam ring 4 rotates, the lens support tube 2 moves along the optical axis, and performs the focus adjustment of the focus adjustment optical system L1, L2.
The manual focus adjustment mode will now be described below. When the lens barrel is in the manual focus adjustment mode, the mode changeover switch 20 slides in the M direction in FIG. 3. By moving the mode changeover switch 20 in the M direction, the electrical power supply to the surface wave motor Mo is cut off.
When the mode changeover switch 20 slides in the M direction, the changeover plate 21 fixed to the mode changeover switch 20 moves at the same time, and presses down the plate spring 22, which is fixed to the fixed barrel 1. By pressing the plate spring 22 downward, the plate spring 22 separates from the engagement grooves 6a in the outer circumferential portion of the fixed element 6.
When the engagement grooves 6a and the plate spring 22 are separated, the hand-operated ring 10 is rotatable. Furthermore, because the electric power supply to the surface wave motor Mo is cut off, the surface wave motor Mo does not drive, and the fixed element 6 and the rotary element 9 are in a state in which they are forcibly pressed by the biasing member 14.
Furthermore, because the frictional torque A of the fixed element 6 and the rotary element 9, and the torque required to drive the lens support tube 2, satisfy the condition C&lt;A, the fixed element 6 and the rotary element 9 rotate integrally via the intermediate ring 7 when the hand-operated ring 10 rotates.
When the rotary element 9 rotates, the rotary element 9 and the cam ring 4 rotate integrally because the engagement groove 9a of the left-hand side of the rotary element 9 is engaged with the engagement projection 4d on the cam ring 4. When the cam ring 4 rotates, the lens support tube 2 moves in the optical axis direction, and the focus adjustment optical system L2, L3 performs focus adjustment.
When the prior art lens barrel having a built-in surface wave motor is in the automatic focus adjustment mode, the mode changeover switch 20 is in the A position, and the engagement grooves 6a in the outer circumferential portion of the fixed element 6 are engaged with the plate spring 22. Because of the engagement of the engagement grooves 6a and plate spring 22, the hand-operated ring 10 is prevented from rotating, and the fixed element 6 is also in a state in which it cannot rotate.
However, even when the engagement grooves 6a and the plate spring 22 are not engaged, the frictional torque B of the fixed barrel 1 and the fixed element 6, and the torque required to drive the lens support tube 2, satisfy the condition C&lt;B. Because of this, the changeover between the automatic focus adjustment mode and the manual focus adjustment mode can be performed in a simple manner according to whether or not electric power is supplied to the surface wave motor Mo.
Accordingly, optional photographic ranges are stored, and after having photographed according to separate photographic ranges, during photography in the automatic focus adjustment mode, a "go-home" photographic function drives the lens to the stored photographic range. When manual focus adjustment is performed, the hand-operated ring 10 is rotated, instantaneously changing over to the manual focus adjustment mode, and mechanical changeover becomes unnecessary. Because of this, it is easy to include a mechanism for rapidly performing a changeover of these functions or modes.
In the prior art lens barrel having a built-in surface wave motor, when Da and Dc in Equation (1) are about equal, the rotation ratio Rr can be set to an optional value by changing the ratio of Db and Db'. Moreover, when Da and Dc are not equal, the rotation ratio Rr can be set to an optional value in the same manner by adjusting all the parameters from Da through Dc. Accordingly, in the prior art lens barrel having a built-in surface wave motor, the angle through which the hand-operated ring 10 is required to rotate, from the .infin. position of the photographic range to the close position, can be set to a sufficient magnitude to perform a delicate manual adjustment, independently of the angle through which the cam ring 4 is rotatable.
However, even though all the parameters from Da through Dc can be adjusted, once the values are set in a manufactured product, it is then impossible to successfully change these values later. Accordingly, the rotation ratio cannot be altered during photography according to the photographic conditions, thus limiting the freedom of focus adjustment.